Newborn Screening
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Direct answer
The heel prick at 48-72 hours — a dried blood spot for TSH, 17-hydroxyprogesterone and, on wider panels, G6PD, galactosaemia, phenylketonuria, biotinidase and tandem-mass-spectrometry markers — exists because the diseases it finds are silent and time-sensitive: congenital hypothyroidism (roughly one in 2500-4000 Indian births) loses IQ by the week, and congenital adrenal hyperplasia can salt-waste to death in week two. India has no universal national programme yet — some states (Kerala, Goa, Chandigarh) and most private hospitals run panels — so the exam frames it "screen early, confirm, treat, don't panic". Two non-blood screens complete the package: hearing (OAE before discharge; the 1-3-6 rule) and critical congenital heart disease by pre- and post-ductal pulse oximetry after 24 hours.
What you must remember
- Timing logic: the 48-72 hour window avoids the physiological TSH surge and the early 17-OHP rise (false positives on day one, especially in preterms and the sick); post-transfusion samples need special interpretation.
- CH screen: raised spot TSH (programme cutoffs 20-40 mIU/L), confirmed by serum TSH and free T4; treatment with levothyroxine 10-15 micrograms/kg/day starts by two weeks — screening converts a cretinism diagnosis into a tablet.
- Congenital adrenal hyperplasia screen: 17-hydroxyprogesterone elevated in 21-hydroxylase deficiency; prematurity, stress and illness raise false positives, and a salt-wasting crisis classically lands at day 7-14 with vomiting, hyponatraemia and hyperkalaemia — the screen aims to precede it.
- Other classic targets: G6PD deficiency (common in India — flags boys at risk of drug and fava-triggered haemolysis), galactosaemia (GALT; soy formula before sepsis and cataracts consolidate), phenylketonuria (rare in India; phenylalanine-free diet), biotinidase deficiency (biotin-responsive) and MS/MS metabolic panels privately.
- Hearing screening: otoacoustic emissions first-line in well babies, BERA confirmatory; the 1-3-6 rule drives language outcomes; congenital hearing loss runs near one to two per thousand, with NICU stay, ototoxic drugs, family history and hyperbilirubinaemia raising risk.
- Critical CHD pulse oximetry: measure in the right hand and either foot after 24 hours of age; positive when saturation is below 90 per cent in either limb, or 90-94 per cent persistently, or the hand-foot difference exceeds 3 per cent — catches ductal-dependent lesions (transposition, hypoplastic left heart, coarctation, TAPVR) before discharge collapse.
- The two-tier rule: a screen is not a diagnosis — an abnormal result triggers a confirmatory test, counselling that avoids catastrophising, and a defined referral.
- Programme reality: universal newborn screening remains aspirational nationally; Rashtriya Bal Swasthya Karyakram delivers facility-based screening for birth defects, and FMGE questions frame screening within such programmes.
What happens after an abnormal TSH
A day-three TSH of 45 mIU/L returns to a district hospital on day eight. The correct sequence: recall the same day, examine (most babies look normal — that is the point of screening), send confirmatory serum TSH and free T4, and if primary hypothyroidism confirms, start levothyroxine 10-15 micrograms/kg/day with free T4 targeted to the upper half of normal. Counsel in one sentence of hope: treated now, intellect is expected to be normal — the tragedy this screen prevents is the infant presenting at six months with developmental delay. Recheck at two and four weeks, and plan the three-year trial-off separating transient from permanent. The same discipline governs all screens: an elevated 17-OHP in a preterm gets a repeat, not a lifetime label.
Where students slip
Timing errors top the list: day-one sampling yields false positives, and the right answer is often "repeat at the correct window" rather than "start treatment". Second, candidates leap from abnormal screen to therapy, forgetting the dried spot is a screen needing confirmation. Third, pulse-oximetry thresholds blur: below 90 per cent positive, grey zone 90-94 per cent or a hand-foot gap above 3 per cent, always after 24 hours. Fourth, OAE screens outer hair cells and misses auditory neuropathy (the kernicterus ear), which BERA catches — a "passed OAE" in a high-risk infant still needs follow-up.
Frequently asked questions
Why is the heel prick taken at 48-72 hours of life?
To avoid the physiological postnatal TSH surge and early 17-hydroxyprogesterone elevation that produce false positives in the first day, while still enabling treatment of time-critical disease within the first weeks.
What is the 1-3-6 rule in newborn hearing screening?
Hearing screening by one month of age, diagnostic audiology by three months, and intervention (hearing aids, implants, therapy) by six months to protect language.
How does pulse oximetry screen for critical congenital heart disease?
Pre-ductal (right hand) and post-ductal (foot) saturations after 24 hours: below 90 per cent in either limb, persistent 90-94 per cent, or a hand-foot difference above 3 per cent is positive and triggers echocardiography.
Which conditions does an Indian private newborn-screening panel usually include?
Congenital hypothyroidism (TSH), congenital adrenal hyperplasia (17-OHP), G6PD deficiency, galactosaemia and, on expanded panels, phenylketonuria, biotinidase deficiency and MS/MS metabolic disorders.
Why must an abnormal screen be confirmed before treatment decisions?
Because dried-spot screening carries false positives from timing, prematurity and stress; confirmatory serum testing plus clinical assessment prevents both missed disease and unnecessary lifelong treatment of a well child.